1921 BIRDS OF MONTANA 63 



where extensive ornithological work has been done except Flathead Lake. It is 

 evidently much commoner on the prairies of the eastern half of the state than in 

 the mountain valleys of the western half. It nests in the Tapper Sonoran and 

 Transition zones, never in the mountains, but only in the valleys of lower foot- 

 hills. It breeds most commonly in cottonwood groves along streams, but also in 

 evergreens growing along the foothills. 



Dates of nesting : The earliest date for eggs in the state is May 7, in Custer 

 County (Cameron, 1913, p. 170). Silloway records a set of three with incuba- 

 tion advanced on May 9, 1903 (1903a, pp. 29-30). Cameron gives June 27 as 

 the latest date he has seen eggs, and Coues (1874b, pp. 625-626) records eggs at 

 the forks of the Milk River, July 16, 1874. According to my experience the 

 majority of birds do not nest until after the middle of May, and nests may be 

 found most commonly in June. The young are out of the nest and able to fly 

 at any time from the first of July to the last of August. 



Migration dates: Gallatin Valley, April 17, 1909. Silver Bow, April 8, 

 1910 (Saunders, 1914a, p. 25). Cameron records a large flight of about 2000 

 birds in Custer County, in April, 1890 (1907, p. 263). Fall dates seem very 

 irregular. Cameron states that the birds leave soon after the young are able to 

 fly. The only fall dates which I have are Sun River, September 27, 1912 

 (1914a, p. 132), and Bridger Mountains, November 18, 1908. 



115. Archibuteo lagopus sancti-johannis (Gmelin) 



Rough-legged Haw^k 



A winter visitor in the mountain valleys and on the prairies. Common 

 locally, and apparently distributed through most of the state, but not reported 

 from the Bitterroot Valley nor from Fergus County. I have found it abundant 

 in winter in the Gallatin Valley (1911a, p. 36), rare in Teton County (1914a, 

 p. 132), and have not observed it in southwestern Montana. In Custer and Daw- 

 son counties it is reported common, but becoming rare (Cameron, 1907, pp. 

 263-264). It is also reported from Fort Custer in February, 1878 (McChesney, 

 1879, p. 2391), and from the vicinity of Billings in winter (Thomas, MS). 



There are a number of summer records of this species, and it possibly breeds, 

 or formerly did so. Cameron records a nest found in the badlands in May, of 

 which the identification is doubtful. Common in summer at Flathead Lake 

 (Silloway, 1901a, p. 46) ; abundant at Gardiner at the end of August (Grinnell, 

 1876, p. 649). 



Migration : In the Gallatin Valley this species first appeared October 9, 

 1908, and was last seen April 17, 1909. 



116. Archibuteo ferrugineus (Lichtenstein) 



Ferruginoi;s Rough-leg 



An abundant summer resident of the prairies in the eastern part of the 



state. Less common in valleys of the mountains, and rather rare west of the 



continental divide. Nearly all observers record it in the eastern regions. It is 



reported to winter in the eastern part of the state, in Custer and Dawson coun- 



